Production of alkyl esters from high free fatty acid sources

ABSTRACT

The invention provides a novel system for the conversion of fats, oils, and greases (FOG) from processed food sources, including but not limited to trap greases, FOG separated from prepared foods, waste streams from glycerin separation processes, “black grease” collected from the scum-layer of waste water treatment facilities, and other sources having high free fatty acid content, to their alkyl esters.

RELATED APPLICATIONS

This application is a continuation of international application PCT/US11/21374 filed Jan. 14, 2011, and claims the benefit of U.S. Provisional Application No. 61/294,879 filed Jan. 14, 2010; the entire disclosures of each are fully incorporated herein.

FIELD OF THE INVENTION

The invention provides a novel system for the conversion of fats, oils, and greases (FOG) from processed food and other sources, including but not limited to trap greases, FOG separated from prepared foods, waste streams from glycerin separation processes, “black grease” collected from the scum-layer of waste water treatment facilities, and other sources having high free fatty acid (FFA) content, to their alkyl esters.

BACKGROUND OF THE INVENTION

Biodiesel comprising the alkyl monoesters of fatty acids from vegetable oils and animal fats may be used as an alternative, non-toxic, biodegradable and renewable diesel fuel. The properties of biodiesel are generally considered quite close to those of ordinary diesel fuel, and can therefore be used in diesel engines with little or no modification. Biodiesel does, however, have certain advantageous characteristics. For example, biodiesel has a higher cetane number than diesel fuel, no aromatics, low to no sulfur, and contains 10 to 11% oxygen by weight. These properties assist in reducing the emission of carbon monoxide, hydrocarbons, and particulate matter in the exhaust as compared to diesel fuel.

Refined vegetable oils are the commonly used primary source materials, or feedstock, for producing biodiesel. In current methods known in the art, methanol is added to vegetable oils to transesterify the triglycerides contained in the feedstock into fatty acid methyl esters (FAME). A base catalyst, such as methoxide, is used to catalyze the transesterification reaction. The use of refined vegetable oils suffers several disadvantages, including the facts that they require processing from otherwise available food sources, and such refined oils are therefore expensive. Cheaper starting materials are desirable for reducing the cost of biodiesel products. Further, suitable feedstock for the conversion process must have a relatively low free fatty acid content, below 15%, which necessarily limits the final yield of resulting converted methyl esters. Thus, the presently preferred source feedstock for the existing conversion process is refined oils.

The cheaper sources of primary materials generally include waste vegetable oils from restaurants and rendered animal fats. On the other hand, high FFA FOG, or fat, oil, and grease is abundant, relatively easy to extract, and inexpensive due to the fact that it is not considered to have substantial food value. High FFA FOG is obtainable from processed food and other sources, including but not limited to trap greases, FOG separated from prepared foods, high FFA residuals from glycerin separation processes, “black grease” collected from the scum-layer of waste water treatment facilities, and other industrial material sources. However, these primary materials are unsuitable for the above-described current methyl ester production process due to their high FFA content, so high FFA FOG must first be processed if it is to be a suitable source feedstock for current processes.

In short, the base catalyst-catalyzed transesterification reaction commonly used for generating FAMEs from refined vegetable oils, fats, and greases cannot be used to produce biodiesel from the cheaper starting materials with high FFA content identified above, such as high FFA FOG, because the materials tend to form soaps with the base catalyst. Some have tried to solve this problem by converting high FFA materials into methyl esters using a large excess amount of methanol and an acid catalyst, and only then proceeding to the commonly used base catalyst-catalyzed transesterification reaction to convert oil to FAMEs. This process is expensive, requires two distinct processes, can require large amounts of methanol, and presents potentially dangerous conditions due to the presence of such large amounts of methanol.

There are many reports indicating the use of acid-catalyzed esterification reactions in the production of lower alcohol esters of waste FOG, especially those materials containing what is deemed to have a high free fatty acid content. Those reports generally employ solid phase acidic sources and/or mineral acids such as phosphoric, hydrochloric and sulfuric for the conversions. These conversions are only a preliminary step in a two-step conversion of the waste FOG into a biodiesel product.

The acid esterification process converts the free fatty acid content of the source FOG to lower alcohol esters. The esterified FOGs are then converted to methyl esters by the classical base-catalyzed trans-esterification reaction, with the production of water and glycerol as by-products. This two-step procedure is necessary in existing production processes because of the formation of soaps (the alkaline salts of free fatty acids), the production of which complicates the production of biodiesel by lowering both yield and quality of the resulting product. The production of water in the reaction also lowers yield and slows the rate of the reactions. The common industry definition of fats, oil and greases having a high free fatty acid content is a considerable variable and can range from lows of below 5% to highs of greater than 90%. Herein, high FFA content means 50-100% FFAs.

Acid-catalyzed esterification of free fatty acids in the waste FOG was reported extensively as a first step in the preparation of biodiesel. See, e.g., Butler, Feb 15, 2007. US 2007/0033863 A1, Ma and Hanna, Bioresource Technology 1999, 70: 1-1; Zhang et al. Bioresource Technology 2003, 89: 1-16; Zhang et al. Bioresource Technology 2008, 99: 8995-8998; Veilkovic et al. Fuel 2006, 85: 2671-2675; Zullaikah et al. Bioresource Technology, 2005, 96: 1889-1896; Ramadhas et al. Fuel 2005, 84: 335-340; Canakci and Van Gerpen, 1999, Trans of ASAE, 42: 1203-1210; US Patent Application Publication No. 2007/0232817; Zafiropoulos et al. 2007, Chem. Commun. 2007, DOI: 10.1039/b704189f.

Included in these acid-catalyzed esterifications are solid phase acidic catalysts. Tungstophosphoric acid, niobic acid as well as mineral supported forms (zirconia, silica, alumina, and activated carbon) have been reported capable of esterification reactions converting FOG to biodiesel. See, e.g., Kulkarni et al. Green Chem. 2006, 8: 1056-1062; Cardoso et al. JAOCS 2008, 10: 1007/s11746-008-1231-0; Caetano et al. Catalysis Comm. 2008, 9: 1996-1999; Chai et al., Advanced Synthesis and Catalysis 2007, 349: 1057-1065; Abdel-Rehim et al., Applied Catalysis A: General: 2006, 305: 211-218; Cao et al., Biotechnol. Bioeng., 2008, 101: 93-100; US Patent Application Publication Number US2007/0232817.

As a sub-division of the acidic conversions are acidic conversions using amorphous carbon materials derived from glucose, such as those reported in Takagaki et al., 2006, Catalysis Today, 116: 157-161; Lou et al., Bioresour. Technol. 2008, 99: 8752-8758; US Patent Application Publication No. 2009/0311709.

U.S. Pat. No. 6,965,044 discloses a process for converting high FFA materials into methyl esters using soapstock residual material produced by the crude oil refining process.

All references cited are incorporated herein in their entirety.

The art of the conversion of waste FOG into biofuels is in need of a process capable of converting high FFA materials into their lower alcohol esters without the drawbacks and limitations of the existing conversion processes, such as the classical two-step process using high lower alcohol to FOG ratios, undesirable production of soap, inability to handle high or even modest FFA content levels, undesirable production of water, and difficult separation of byproducts such as glycerin.

SUMMARY OF THE INVENTION

The inventors herein have improved on known processes which begin with an acid conversion step in order to prepare suitable low FFA feedstock for the base-catalyzed conversion step, by eliminating the need for such two-step acid-catalyzed and base-catalyzed conversions. The present invention provides a single-step process for conversion of FOG materials having high free fatty acids, ranging from 50-100% free fatty acids, into alkyl esters, and thus to biodiesel, without the need of first refining the FOG. Whereas existing methods use multistep approaches, use many reagents that have significantly dangerous aspects, and cannot process truly high free fatty acid FOGs, the present invention may be practiced in a single step conversion allowing recovery of biofuel, alcohol, inorganic salts, modest amounts of glycerin, and unreacted glycerides. The conversion occurs at temperatures at or below the boiling points of the lower alcohols used, with agitation, in a closed system, although the process of the invention may also be practiced at temperatures at or above such boiling points.

In one aspect, the invention provides a simplified, single-step conversion of the high free fatty acid materials in FOGs to their alkyl esters and hence into a biodiesel type fuel. The invention uses an acid catalyst, such as sulfuric acid and phosphoric acid, but not simply for the preparation of lower FFA materials suitable for a base-catalyzed process as in known methods. Instead, the acid catalysis process of the invention directly produces the biofuel from high FFA materials in a single step.

Thus, in one aspect, the present invention provides a method for converting high FFA source material into alkyl esters, comprising the steps of reacting in a reactor vessel a mixture of the source material with an esterification reagent comprising an acid catalyst and an alcohol for a sufficient time to produce alkyl esters; and recovering the alkyl esters.

In another aspect, the source material may be fats, oils, and greases (FOG) from processed food sources, including but not limited to trap greases, FOG separated from prepared foods, and waste streams from glycerin separation processes.

In another aspect, the acid catalyst is selected from the group consisting of sulfuric acid and phosphoric acid. The alcohol is an alkyl alcohol, generally a lower alkyl alcohol, generally methanol or ethanol. In another aspect, the alkyl esters produced are methyl esters.

In another aspect, the reaction product may be washed, allowing recovery of at least one of salts of the acid catalyst, glycerin, and water.

In another aspect, the esterification reaction step is performed at a temperature of at least the boiling point of the alcohol, or at ambient temperature, or at a temperature between 5-65° C. In another aspect, the esterification reaction step is performed at ambient pressure, or a pressure between 15-60 psi.

In another aspect, the FFA content of the source material is greater than 50%, or 65%, or 75%, or 85%, or 95%.

In another aspect, greater than 90% of the FFAs are esterified to alkyl esters, or greater than 95%, or greater than 97%.

In yet another aspect, a preliminary feedstock having lower FFA content is first converted to the high FFA source material.

These and additional features of the invention are exemplified and further described in the Detailed Description of the Invention below.

DETAILED DESCRIPTION OF THE INVENTION

As described above in the Summary of the Invention, the invention provides a simplified, single-step conversion of the high FFA materials in FOGs to their alkyl esters and hence into a useful biodiesel-type fuel.

Source Materials

The method of the invention is suitable for the conversion of high FFA materials, including those from FOG. In general, the invention is suitable for conversion of FFA materials comprising between about 50-100% free fatty acid content, preferably between about 60-100%, more preferably between about 65-95% free fatty acid content. Trap greases, FOG separated from prepared foods, “black grease” collected from the scum-layer of waste water treatment facilities, waste streams from glycerin separation processes, and any high FFA industrial residue materials, are all suitable primary source materials. The FFAs in the source material are esterified to a substantially high degree of completion, greater than about 90% completion, preferably greater than 95%, more preferably greater than 97%.

While the process of the invention is capable of direct conversion of high FFA starting materials to biofuel, the process is also capable of esterifying lower FFA content starting materials to a similar level of completion, that is, greater than about 90% completion, preferably greater than 95%, more preferably greater than 97%. However, where the starting material has lower FFA content, other materials (e.g., fats) in the source material may well prevent the esterifying reaction product from being useful directly as biofuel without removal thereof. Thus, in another embodiment, lower FFA content preliminary feedstock material may be first converted to higher FFA source material by, for example, converting the fats therein to FFAs, thereby rendering the source material into a suitable material for direct production of biofuel through the process of the invention.

Reagents

The process of the invention uses an acid catalyst, such as, but not limited to, sulfuric acid and phosphoric acid. Hydrochloric acid is generally not preferred nor is nitric acid. Organic acids are not recommended because they tend to increase reaction time and also present problems with a large number of side reactions and products. Other suitable catalysts include, but are not limited to, dimethyl sulfate, methyl hydrogen sulfate, and methyl sulfonic acid; however, those of skill in the art will appreciate that the choice of acid catalyst should be tempered with awareness of any toxicity and explosion potential of such catalysts, and should handle such catalysts with appropriate safety procedures. The amount of acid catalyst used is a function of the FFA content of the source material. In general, the concentration of acid ranges from 0.5N to 4N, preferably 2N, prepared in a lower-alcohol, preferably lower alkyl alcohols, preferably methanol or ethanol. Most preferably, the lower alkyl alcohol is methanol. In one embodiment, the methanol component of the esterification reagent may be commercial or reagent grade. In another embodiment, in which ethanol is used, the ethanol may be reagent grade or the 95% denatured product, or the like.

In one embodiment, sulfuric acid is used and the preferred concentration may be prepared using the generally available 98% or 93% commercial materials. In another embodiment, a phosphoric acid catalyst is prepared, generally from the 85% commercial material or the like.

In general, the esterification reagent—acid catalyst and alcohol—is premixed, and added to the source material. The amount of reagent to add to source material ranges from as little as 15% to as much as 100% of the volume of the feedstock. The choice of the volume is, at least in part, dependent upon the desirability or necessity to recover the unreacted alcohol. The speed of the reaction can be dependent on the excess concentration of the process reagent.

Conversion Process and Reaction Parameters

In one embodiment, the conversion process begins with exposure of source materials with high FFA content to the esterification reagent prepared as described above.

The source material, having high free fatty acid content, is monitored into a reactor vessel. The source material may require heating to allow easy pouring and should contain <2% moisture and minimal suspended solids. When necessary, the source material should be screened/filtered of gross solids and separated from any aqueous fractions. The volume of the esterification reagent to be added ranges from 15% to 100% volume/volume. The preferred reaction occurs with mixing (stirring, cavitation or sheer forces), equivalent to 200 rpm, at temperatures at or approaching the boiling point of the alcohol used. Thus, when using methanol, the reaction occurs at a temperature of about 65° C., while when using ethanol, the reaction occurs at a temperature of about 85° C.

In an alternative embodiment, the reaction is carried out at ambient temperatures, 18-25° C. The reaction will take longer than when performed at higher temperatures, up to about 4 days.

In another embodiment, the reaction may be carried out at higher temperatures, such as 35-60° C. The reaction vessel is sealed and the reaction is allowed to proceed to completion, one to three days. Alternatively, the reaction may be carried out at temperatures exceeding the boiling point of the alcohol, in which case the reaction reaches completion in a much shorter time, from 15 minutes to an hour.

After the esterification reaction is completed, the reaction mixture is allowed to cool to ambient temperature by cooling from external sources. The reaction products include the alkyl esters of the free fatty acids in the source material, unused acid catalyst and alcohol, particulates, glycerin, unconverted fats, and moisture. The alkyl esters are preferably methyl or ethyl esters, though other alkyl esters may be produced if desired by using the appropriate alcohols and temperatures. For example, when ethyl esters are desired, the reaction is performed with ethanol. In one embodiment, the reaction is performed with at least 25-30% esterification reagent, vol/vol to source material, and proceeds at or about 85° C.

After the reaction is completed the mixture is usually washed as described below to remove impurities. Regardless of the percentage of free fatty acid content of the feedstock, the described process is capable of reacting the FFA fraction to a 99%+esterification, provided the proper balance of time, temperature, and reagent concentration is observed. The process will not react with or esterify glyceride molecules comprising the remaining fraction of the starting material.

Washing

The reaction mixture must be washed or rinsed to remove excess acid, alcohol, and glycerin. Solutions of calcium hydroxide, calcium oxide, or even slaked lime or cement kiln materials may be used. In one embodiment, concentrations of washing agent to be used should be equivalent to calcium hydroxide at 1.0 g/L. Reasonably purified water should be used, such as that which has undergone ion exchange or other water softening systems. Aqueous calcium hydroxide is particularly useful in this washing step because it neutralizes any excess acid and precipitates any remaining sulfate or phosphate as highly insoluble calcium salts. Other washing agents may alternatively be used. The washing step separates the relatively small amounts of glycerin formed from the esterification reaction, which can then be recovered. Unreacted alcohol can be recovered by, for example, distillation processes. The product, the lower alcohol esters of the mixed fatty acids, after washed, can be separated from the aqueous phase by gravitational separation, usually requiring 24 hours at 40° C., and/or centrifugation. Entrapped moisture, if a problem, may be removed by various dehydration techniques, for example, media column extraction may be used, heating past 100° C. or 212° F., and relying on gravity.

Conversion of the high free fatty acid source materials to esters results in a biofuel product containing at least as low as 10% or less free fatty acids. Preferably, the remaining free fatty acid content is 5% or less, consistent with certification requirements for biofuel, more preferably 2% or less, more preferably 1.5% or less. Thus the resulting product is suitable for use as biofuel.

The invention is further exemplified by the following illustrative and non-limiting Examples.

EXAMPLES Example 1

An Example Process of the Invention Using Methanol

In this example, the esterification reagent comprised 2N H₂SO₄ acid, in methanol. Fifty ml of molten brown grease containing 74% FFA were placed into a glass 250 ml Erlenmeyer flask fitted with a ground glass neck. Fifteen ml of esterification reagent (i.e., 30% vol/vol of source grease), and a stir bar were added to the grease. A ground glass stopper was used as a closure to ensure a gas-tight seal. The flask was placed atop a stir plate with the mechanism adjusted to a medium stir rate of approximately 200-rpm, inside an incubator set at 65° C. for three hours. After 3h the flask was removed from the incubator and allowed to cool at room temperature. To the contained reaction mixture, 10 ml of Ca(OH)₂ (calcium hydroxide) rinsing agent was added, and placed on a stir plate operating at about 400-rpm for 3 minutes. The reaction mixture was transferred to tubes and centrifuged in a benchtop centrifuge allowing the fuel to separate from the rest of the mixture. A small portion (5 ml) of the fuel product was removed from the tubes to determine the level of completion of the reaction by potassium hydroxide titration. The product contained 2.17% FFA, signaling a 97+% conversion of the 74% FFA start material.

Example 2

An Example Process of the Invention Using Methanol

In this example, the esterification reagent comprised 2N H₂SO₄ acid, in methanol. Two liters of molten brown grease containing 93% FFA were placed into a glass 4-L Erlenmeyer flask with 800 ml (40%) of esterification reagent, and a stir bar. A rubber stopper was affixed to the flask, and taped securely to ensure a tight seal. The flask was placed atop a stir plate with the mechanism turned to a medium stir rate (approximately 200-rpm), inside a water jacketed incubator set at 54° C. for two days. After 48 h the flask was removed from the incubator and allowed to cool to room temperature. To the contained reaction mixture 600 ml of Ca(OH)₂ (calcium hydroxide) rinsing agent was added, and placed on a stirring plate operating at about 400-rpm for 30 minutes. The reaction mixture was removed to a separatory funnel which was placed in a 40° C. water bath for 24 h, allowing the fuel to separate from the rest of the mixture. A small portion (5 ml) of the fuel product was removed from the separatory funnel to determine the level of completion of the reaction by potassium hydroxide titration. The product contained 1.86% FFA, signaling a 98+% conversion of the 93% FFA start material.

Example 3

An Example Process of the Invention at Higher Temperature

In this example, the esterification reagent comprised 2N H₂SO₄ acid, in methanol. Fifty ml of molten brown grease containing 74% FFA were placed into a 250 ml Erlenmeyer flask having a ground glass neck. Fifty ml of esterification reagent (100%) was added to the grease. The flask was placed into a hot water bath at 100° C. after fitting with a reflux condenser, and allowed to reflux for three hours. After 3 h the flask was removed from the boiling water bath and allowed to cool. To the contained reaction mixture 10 ml of Ca(OH)₂ (calcium hydroxide) rinsing agent was added, and placed on a stirring plate operating at 400-rpm for 3 minutes. The reaction mixture was transferred to tubes and centrifuged in a benchtop centrifuge allowing the fuel to separate from the rest of the wash mixture. A small portion (5 ml) of the fuel product was removed from the tubes to determine the level of completion of the reaction by potassium hydroxide titration. The product contained 0.62% FFA, signaling a 99+% conversion of the 74% FFA start material.

Example 4

Temperature Variations

In each production run of this example, at the specified temperatures, the esterification reagent mixture consisted of 2N H₂SO₄ acid in methanol prepared from the 98% commercial materials. Examples 4a, 4b, and 4c used reagent volumes (vol. reagent mixture to vol. source material) of 25 and 50%; example 4d used reagent volume of 20, 30, 40, and 50%; example 4e used a 40% reagent volume; and example 4f used a 100% reagent volume. Reaction temperature and length of reaction vary, illustrating the influence of time, temperature, and reagent concentration on esterification. The extent of esterification was measured by potassium hydroxide titration, to determine the remaining FFA % of the washed product, and thereby determine the extent of completion of the reaction.

Example 4a

TABLE 1 Remaining FFA % after ambient temperature production conducted at 25° C., over three days: Reagent volume v/v % Day 1 Day 2 Day 3 50 14.9 7.4 6.7 25 25.4 18.9 14.6

Example 4b

TABLE 2 Remaining FFA % after elevated ambient temperature production conducted at 37° C., over three days: Reagent volume v/v % Day 1 Day 2 Day 3 50 8.4 1.6 0.93 25 19.2 10.5 6.2

Example 4c

TABLE 3 Remaining FFA % after elevated temperature production conducted at 45° C., over three days: Reagent volume v/v % Day 1 Day 2 Day 3 50 1.9 0.93 0.93 25 11.5 6.5 3.7

Example 4d

TABLE 4 Remaining FFA % after elevated temperature production conducted at 56° C., over two days: Reagent volume v/v % Day 1 Day 2 20 5.6 3.7 30 2.2 2.2 40 1.6 1.2 50 1.2 0.9

Example 4e

In this production run, illustrating a reaction at or above the gas-phase temperature of methanol (65° C.), the reaction was run using a 40% reagent volume, at 65° C. for 3 hours, and produced an end product containing 2.17% FFA.

Example 4f

In this production run using a 100% reagent volume, the reaction proceeded at 100° C. for 1.5 hours, and the end product contained 0.62% FFA.

Example 5

Large Scale Process of the Invention

In this example, the esterification reagent comprised 2N H₂SO₄ acid, in methanol. Five hundred liters of molten brown grease containing 93% FFA was placed into an airtight, glass-lined stainless steel reactor designed with a mechanized glass coated stir paddle. One hundred fifty liters of esterification reagent (30% vol./vol.) was added to the grease. The stir mechanism was set at a stir rate of 200-rpm, and the jacket temperature was set at 80° C. for two hours. After 2 h a small portion (5 ml) of the fuel product was removed from the reactor to determine the level of completion of the reaction by potassium hydroxide titration.

Generally, if the level of completion as measured is less than desired, the reaction may be permitted to continue for additional times of 15 minutes, or 30 minutes, or more. A potassium hydroxide titration may then be performed again to measure the level of completion. Once determined to be complete, or as complete as desired, which in this case was reached at the end of the initial 2 hour period, the contents of the reactor was transferred by AOD pump to a polyethylene cone bottom mixing tank, where 100 liters of Ca(OH)₂ (calcium hydroxide) rinsing agent was added, and the mixture was agitated by AOD pump cycling for 1 hour. The reaction mixture was transferred to polyethylene cone bottom tanks allowing the fuel to separate from the rest of the mixture at 40° C. for two days. A small portion (5 ml) of the fuel product was removed from the separated fuel to confirm the level of completion of the reaction by potassium hydroxide titration. The product contained 0.93% FFA, signaling a 99+% conversion of the 93% FFA start material, and a 95%+recovery of the start volume.

Example 6

Small Batch Commercial Production of the Invention

In this example, the esterification reagent comprised 2N H₂SO₄ acid, in methanol. Thirteen hundred and twenty five liters of molten brown grease containing 98% FFA is measured into a twenty eight hundred forty liter glass-lined stainless steel reactor designed with a mechanized glass coated stir paddle. Three hundred thirty three liters of esterification reagent (˜25%) were added to the grease. The stir mechanism was set at a stir rate of 200-rpm for three hours, and the internal reactor temperature was set at 80° C. After 2 h, and at half-hour intervals thereafter, a small portion (5 ml) of the fuel product was removed from the reactor to determine the level of completion of the reaction by potassium hydroxide titration. The product of the reaction was determined to contain 3.5% FFA.

The reaction was permitted to continue for an additional half hour, at which time another aliquot was removed and its FFA content measured by potassium hydroxide titration. The product then contained 2.1% FFA. Another additional half hour reaction time brought the level of FFA to 0.97%, at which point, the contents of the reactor was transferred by AOD pump to a thirty seven hundred liter polyethylene cone bottom mixing tank, where three hundred eighty liters of Ca(OH)₂ (calcium hydroxide) rinsing agent was added. The mixture was agitated by AOD pump cycling for 1 hour. The reaction mixture was transferred to polyethylene cone bottom tanks allowing the fuel to separate from the rest of the mixture, maintaining a 40° C. internal temperature for two days.

A small portion (5 ml) of the fuel product was removed from the separated fuel to confirm the level of completion of the reaction by potassium hydroxide titration. The product contains 0.97% FFA, signaling a 99+% conversion of the 98% FFA start material, and a 95%+recovery of the start volume as fuel.

It will be apparent to persons skilled in the art that numerous enhancements and modifications can be made to the above described apparatus without departing from the basic inventive concepts. All such modifications and enhancements are considered to be within the scope of the present invention, the nature of which is to be determined from the foregoing description and the appended claims. Furthermore, the preceding Examples are provided for illustrative purposes only, and not intended to limit the scope of the invention. All references cited are incorporated herein in their entirety. 

We claim:
 1. A method for converting high FFA source material into alkyl esters, comprising the step of: (a) reacting in a reactor vessel a mixture of the source material with an esterification reagent comprising an acid catalyst and an alcohol for a sufficient time to produce alkyl esters.
 2. The method of claim 1, further comprising the step of: (b) recovering the alkyl esters.
 3. The method of claim 1, wherein the source material is at least one member selected from the group consisting of fats, oils, and greases (FOG) from processed food sources, including but not limited to trap greases, FOG separated from prepared foods, “black grease” collected from the scum-layer of waste water treatment facilities, and waste streams from glycerin separation processes.
 4. The method of claim 1, wherein the acid catalyst is selected from the group consisting of sulfuric acid and phosphoric acid.
 5. The method of claim 1, wherein the alcohol is an alkyl alcohol.
 6. The method of claim 5, wherein the alcohol is methanol.
 7. The method of claim 5, wherein the alcohol is ethanol.
 8. The method of claim 1, wherein the alkyl esters are methyl esters.
 9. The method of claim 1, further comprising the step of washing and recovering at least one of the group consisting of salts of the acid catalyst, glycerin, and water.
 10. The method of claim 1, wherein step (a) is performed at at least the boiling point of the alcohol.
 11. The method of claim 1, wherein step (a) is performed at ambient temperature.
 12. The method of claim 11, wherein the temperature is between 5-65° C.
 13. The method of claim 1, wherein step (a) is performed at ambient pressure.
 14. The method of claim 1, wherein step (a) is performed at a pressure between 15-60 psi.
 15. The method of claim 1, wherein the FFA content of the source material is greater than 50%.
 16. The method of claim 15, wherein the FFA content of the source material is greater than about 75%.
 17. The method of claim 15, wherein the FFA content of the source material is greater than about 90%.
 18. The method of claim 1, wherein greater than 90% of the FFAs are esterified to alkyl esters.
 19. The method of claim 1, wherein greater than 95% of the FFAs are esterified to alkyl esters.
 20. The method of claim 1, wherein greater than 97% of the FFAs are esterified to alkyl esters.
 21. The method of claim 1, wherein greater than 99% of the FFAs are esterified to alkyl esters.
 22. The method of claim 1, wherein a preliminary feedstock having lower FFA content is first converted to the high FFA source material. 